linux-kernel - Re: [PATCH -v3 6/7] kexec jump: __ftrace_enabled

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Date:	Mon, 18 Aug 2008 09:59:37 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Machek <pavel@....cz>, nigel@...el.suspend2.net,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH -v3 6/7] kexec jump: __ftrace_enabled_save/restore


* Huang Ying <ying.huang@...el.com> wrote:

> On Fri, 2008-08-15 at 14:49 +0200, Ingo Molnar wrote:
> > * Huang Ying <ying.huang@...el.com> wrote:
> > 
> > > +/* Ftrace disable/restore without lock. Some synchronization mechanism
> > > + * must be used to prevent ftrace_enabled to be changed between
> > > + * disable/restore. */
> > 
> > use the proper comment style please:
> > 
> > /*
> >  *
> >  */
> 
> OK. I will change it.

it's upstream already, please send a followup clean up patch.

> > > +static inline int __ftrace_enabled_save(void)
> > > +{
> > > +#ifdef CONFIG_FTRACE
> > > +	int saved_ftrace_enabled = ftrace_enabled;
> > > +	ftrace_enabled = 0;
> > > +	return saved_ftrace_enabled;
> > > +#else
> > > +	return 0;
> > > +#endif
> > > +}
> > > +
> > > +static inline void __ftrace_enabled_restore(int enabled)
> > > +{
> > > +#ifdef CONFIG_FTRACE
> > > +	ftrace_enabled = enabled;
> > > +#endif
> > > +}
> > 
> > hm, what is this used for?
> > 
> > also, instead of such an ugly inline, why not create a proper 
> > kernel/trace/* function for this. That would also give it access to all 
> > the proper locking mechanisms - instead of relying on some extral 
> > mechanism.
> 
> This function is used for kexec jump in machine_kexec(). Where all 
> non-boot CPUs and IRQ are disabled, system is going to kexec, and it 
> is not allowed to schedule to other process in this circumstance, so a 
> non-lock version is needed. A locked version has been implemented by 
> Steven Rostedt, I think it can be used for other circumstance.

ok, fair enough.

	Ingo
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